Strong box



FIG. 1 is a front, top perspective view of a strong box showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is another perspective view thereof.

The broken lines shown in the drawings represent portions of the strong box that form no part of the claimed design. 

CLAIM The ornamental design for a strong box, as shown and described. 